1. Field of the Invention
The present invention relates to a method for optically recording/reproducing data to/from a recording medium such as an optical card, the method especially having a detecting process for detecting recording/reproducing power of a laser beam when data is recorded/reproduced by the laser beam.
2. Description of the Related Art
Conventionally, data recording has been performed by a laser beam irradiated onto a recording medium from a semiconductor laser, and the recording medium is physically deformed or altered by the heating function.
However, there is a case in which output power efficiency is often changed by temperature change of the surroundings of the laser beam or other ambient changes.
Therefore, a method is required for keeping constant the output power of the laser beam. For example, the output power of the laser beam is detected at a predetermined timing and the detected data is compared with a target value, and the compared data is fed-back to a semiconductor laser driving circuit. Then, in order to obtain a value which is close to the target value, the semiconductor laser is controlled so that the output power of the laser beam is constantly maintained.
As a specific example, Published Unexamined Japanese Patent Application (PUJPA) No. 58-40878 discloses a method for driving a semiconductor laser.
In the method described in PUSPA No. 58-40878 (a pulse is superimposed on a DC bias, whereby the semiconductor laser is driven), the respective light-emitting outputs of the DC bias and a DC bias to which the pulse is applied are separately monitored, and the laser beam is controlled in accordance with the result of the monitoring and the output power of the laser beam is thereby controlled.
In the above-mentioned method, in a case where data is reproduced, since the output power of the semiconductor laser is set to a predetermined constant value, the control of the semiconductor laser is relatively easily performed.
However, problem areas when the data recording is performed in such a manner that the output power of the laser beam is modulated. Due to this, in order to detect the recording power during the recording, a circuit for detecting the recording power is required. As a result, the entire circuit is enlarged.
Therefore, this prior art provides a simple method, in which that the output power of the laser beam is directly changed to the recording power.
However, since the recording power has a higher output, there are cases when the recording medium is often broken or damaged.
As an example to overcome the above-mentioned problems, there is a recording power detection method, which is disclosed in Published Unexamined Japanese Patent Application (PUJPA) No. 61-253651.
According to the above method, the semiconductor laser is controlled so that an optical head is moved to a position other than a recording region of an optical disc by head moving means, thereby directly outputting the recording power. Then, the output value is compared with the target value and detected whether the recording power is excessive or too small, thereby controlling the recording power to be close to the target value.
According to the above method, the detection of the output power is performed when the recording medium is inserted or discharged. Due to this, in a case where the environment around the laser beam is changed after inserting the recording medium and the recording power must be detected again, the recording medium must be discharged again or the optical head must be moved.
As mentioned above, according to the above method, the optical head and the recording medium are relatively moved, thereby the output power is controlled. Due to this, even if the laser beam is focused on a predetermined recording track of the recording medium, the optical head must be once moved to the outside of the recording region of the recording medium in order to detect the recording power. As a result, to perform a next access, the operation must be started again from a coarse seek operation.